Interface switch for distributed energy resources

• US 7,521,825 B2
• Filed: 11/04/2005
• Issued: 04/21/2009
• Est. Priority Date: 11/04/2005
• Status: Active Grant

• Current Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Original Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Inventors: Piagi, Paolo, Lasseter, Robert H.
• Primary Examiner(s): Jackson; Stephen W
• Assistant Examiner(s): KAPLAN, HAL IRA
• Application Number:
  US11/266,976
• Publication Number:
  US 20070129110A1
• Time in Patent Office: 1,264 Days
• Field of Search: 307/126, 307/127, 307/129, 307/130
• US Class Current: 307/130
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers

Abstract

A method and apparatus for an interface switch having an external terminal electrically connected to an AC voltage Ē at a frequency ω₀ (for example a utility supply), and an internal terminal electrically connected to an AC voltage V at a selectable frequency ω (for example a microsource). In one embodiment, the interface switch is closed when the voltage difference between Ē and V and the relative phase angle δ_EV between Ē and V are both small, and when the higher frequency voltage (as between Ē and V) leads the lower frequency voltage. In another embodiment, the interface switch is closed when the envelope of the voltage difference between Ē and V reaches a local minimum at a point of inflection.

Claims

1. A method of operating an interface switch associated with a microgrid, the method comprising:

receiving an AC voltage V at an internal terminal of the interface switch from a microsource bus, wherein the internal terminal of the interface switch is electrically connected to the microsource bus, and further wherein an external terminal of the interface switch is electrically connected to a supply bus having an AC voltage Ē

;

determining a voltage difference between the AC voltage Ē and

the AC voltage V when the interface switch is in an open position;

determining a relative phase angle δ

_EV between the AC voltage Ē and

the AC voltage V while the interface switch is in the open position;

closing the interface switch upon detection that the voltage difference between the AC voltage Ē and

the AC voltage V is less than a first predetermined threshold, the relative phase angle δ

_EV between the AC voltage Ē and

the AC voltage V is less than a second predetermined threshold, and the AC voltage Ē

leads the AC voltage V; and

importing electrical power from the supply bus to the microsource bus through the closed interface switch.

2. The method of claim 1, wherein the first predetermined threshold comprises 10% of an average peak value of the AC voltage Ē

.

3. The method of claim 1, wherein the first predetermined threshold comprises 3% of an average peak value of the AC voltage Ē

.

4. The method of claim 1, wherein the second predetermined threshold comprises 10 degrees.

5. The method of claim 1, wherein the second predetermined threshold comprises 3 degrees.

6. The method of claim 1, wherein the supply bus receives the AC voltage Ē

directly or indirectly from a utility grid.

7. A method of operating an interface switch associated with a microgrid, the method comprising:

receiving an AC voltage V at an internal terminal of the interface switch from a microsource bus, wherein the internal terminal of the interface switch is electrically connected to the microsource bus, and further wherein an external terminal of the interface switch is electrically connected to a supply bus having an AC voltage Ē

;

determining a voltage difference between the AC voltage Ē and

the AC voltage V when the interface switch is in an open position;

determining a relative phase angle δ

_EV between the AC voltage Ē and

the AC voltage V while the interface switch is in the open position;

closing the interface switch upon detection that the voltage difference between the AC voltage Ē and

the AC voltage V is less than a first predetermined threshold, the relative phase angle δ

_EV between the AC voltage Ē and

the AC voltage V is less than a second predetermined threshold, and the AC voltage V leads the AC voltage Ē

; and

exporting electrical power from the microsource bus to the supply bus through the closed interface switch.

8. The method of claim 7, wherein the first predetermined threshold comprises 10% of an average peak value of the AC voltage Ē

.

9. The method of claim 7, wherein the first predetermined threshold comprises 3% of an average peak value of the AC voltage Ē

.

10. The method of claim 7, wherein the second predetermined threshold comprises 10 degrees.

11. The method of claim 7, wherein the second predetermined threshold comprises 3 degrees.

12. The method of claim 7, wherein the supply bus receives the AC voltage Ē

from a utility supply.

13. An interface switch comprising:

an internal terminal configured to connect to an internal power bus bearing an AC voltage V;

an external terminal configured to connect to an external power bus bearing an AC voltage Ē

;

a controllable electrical switch between the internal terminal and the external terminal, the controllable electrical switch having an open condition wherein the internal terminal is electrically isolated from the external terminal and a closed condition wherein the internal terminal is electrically connected to the external terminal; and

a switch controller configured to control the controllable electrical switch by placing the controllable electrical switch into the open condition or the closed condition, wherein the switch controller is configured to determine a voltage difference between the AC voltage Ē and

the AC voltage V and a relative phase angle δ

_EV between the AC voltage Ē and

the AC voltage V, and further wherein the switch controller is configured to close the controllable electrical switch upon detection that the voltage difference is less than a first predetermined threshold, the relative phase angle δ

_EV is less than a second predetermined threshold, and the AC voltage Ē

leads the AC voltage V such that electrical power is imported to the internal bus from the external bus through the controllable electrical switch.

14. The interface switch of claim 13, wherein the switch controller is further configured to close the controllable electrical switch when the AC voltage Ē

leads the AC voltage V and ω

≧

ω

₀, wherein ω

is a selectable frequency of the AC voltage V and ω

₀ is a frequency of the AC voltage Ē

.

15. The interface switch of claim 13, wherein the first predetermined threshold comprises 10% of an average peak value of Ē

.

16. The interface switch of claim 13, wherein the second predetermined threshold comprises 10 degrees.

17. The interface switch of claim 13, wherein the AC voltage Ē

is supplied by a utility supply, and wherein the AC voltage V is supplied by a microsource.

18. A method of operating an interface switch in a microgrid, the method comprising:

receiving an AC voltage V at an internal terminal of the interface switch from an internal bus, wherein the internal terminal is electrically connected to the internal bus, and further wherein an external terminal of the interface switch is electrically connected to an external bus bearing an AC voltage Ē

;

determining an envelope of a waveform corresponding to a voltage difference between the AC voltage Ē and

the AC voltage V while the interface switch is in an open position; and

closing the interface switch at or just after a time when the envelope of the waveform of the voltage difference between the AC voltage Ē and

the AC voltage V reaches a local minimum at a point of inflection.

19. The method of claim 18, wherein the AC voltage Ē

is supplied directly or indirectly by a utility supply.

20. The method of claim 19, wherein the AC voltage Ē

has a frequency of 60 Hz.

21. The method of claim 18, wherein the AC voltage V is supplied directly or indirectly by a microsource.

22. An interface switch comprising:

an internal terminal configured to connect to an internal power bus bearing an AC voltage V at a selectable frequency ω

;

an external terminal configured to connect to an external power bus bearing an AC voltage Ē

at a frequency ω

₀;

a controllable electrical switch between the internal terminal and the external terminal, the controllable electrical switch having an open condition wherein the internal terminal is electrically isolated from the external terminal and a closed condition wherein the internal terminal is electrically connected to the external terminal; and

a switch controller configured to control the controllable electrical switch by placing the electrical switch into the open condition or the closed condition, wherein the switch controller is configured to identify an envelope of a waveform corresponding to a difference between the AC voltage Ē and

the AC voltage V, and further wherein the switch controller is configured to close the controllable electrical switch at or just after a time when the envelope of the waveform of the voltage difference between the AC voltage Ē and

the AC voltage V reaches a local minimum at a point of inflection.

23. The interface switch of claim 22, wherein the AC voltage Ē

is supplied directly or indirectly by a utility supply.

24. The interface switch of claim 23, wherein ω

₀ is 60 Hz.

25. The interface switch of claim 22, wherein the the AC voltage V is supplied directly or indirectly by a microsource.